This Invention relates to a device for dispensing or injecting a controlled amount of desired liquid chemical into a well. Wells, and particularly oil wells, rely upon the downhole injection of chemicals, including surfactants, corrosion inhibitors, foaming chemicals, and the like to enhance well production.
Existing methods of injecting chemicals into wells include direct injection through the use of a simple check valve placed in a tubing string inserted into the well, with the operation of the valve depending on a balance of the downhole pressure, hydrostatic column pressure of the chemical in the tubing string, and additional injection pressure exerted on the inserted chemical. Due to the enormous pressures at typical oil well depths, these valves are inadequate to survive the environment and are frequently subject to back flow of downhole chemicals, gases, and fluids. Many of these chemicals are highly corrosive and are damaging to equipment once a back flow occurs. Furthermore, with these existing systems, chemicals must be inserted through the tubing at a hydrostatic pressure higher than the downhole pressure; most existing equipment is not designed to withstand the stresses involved. Furthermore, because the downhole pressure can vary widely, the hydrostatic column pressure can sometimes exceed the downhole pressure, allowing chemical to flow freely until the differential between the downhole pressure and the hydrostatic column pressure is sufficient to stem the free flow of chemical into the well. This free flow of chemical, combined with the regular inconsistent chemical injection associated with traditional check valves, leads to substantial waste of chemicals injected into the well. This wasted chemical is often expensive; furthermore, in some cases, an excess of injected chemical can be more harmful than helpful. A need exists, therefore, for an apparatus capable of delivering a steady, measured quantity of liquid chemical into a well without regard to the downhole pressure or the hydrostatic column pressure of chemical in the downhole tubing string.